Imaging apparatus, imaging system, and method for driving imaging apparatus

ABSTRACT

The imaging apparatus has a plurality of pixels each of which has a plurality of photoelectric conversion units; generates a plurality of first combined signals obtained by combining signals based on electric charges of photoelectric conversion units in one side with each other, and a plurality of second signals obtained by combining signals based on electric charges of the plurality of photoelectric conversion units with each other; and outputs a part of the first combined signals out of the plurality of first combined signals.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an imaging apparatus, an imagingsystem, and a method for driving the imaging apparatus.

Description of the Related Art

An imaging apparatus is known which has a plurality of pixels containinga plurality of photoelectric conversion units arranged under the samemicrolens, and outputs a signal based on one photoelectric conversionunit and a signal based on another photoelectric conversion unit. Thisimaging apparatus uses signals of at least two photoelectric conversionunits provided under the same microlens, measures a phase difference,detects a focus. Furthermore, the imaging apparatus adds up the signalsof the above described two photoelectric conversion units, and therebyobtains an imaging signal. For instance, Japanese Patent ApplicationLaid-Open No. 2013-090160 discloses a technology of adding and readingout signals per pixel unit and solely reading out a signal from eachphotoelectric conversion unit, in an imaging element in which each pixelhas a plurality of photoelectric conversion units and which reads outsignals sent from the respective pixels.

However, in Japanese Patent Application Laid-Open No. 2013-090160, astudy has not sufficiently been conducted for increasing the speed ofreading out an added signal of signals based on the plurality ofphotoelectric conversion units, and reading out a signal for measuring aphase difference, which is sent from a part of the plurality ofphotoelectric conversion units.

The technology that will be described below relates to an imagingapparatus, an imaging system and a method for driving the imagingapparatus, which can increase the speed of an operation.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, an imaging apparatuscomprises: a plurality of pixels, arranged in a matrix, each including aplurality of photoelectric conversion units generating an electriccharge based on an incident light; a controlling unit configured tocontrol each of the plurality of pixels to output a first signal basedon an electric charge accumulated in one of the plurality ofphotoelectric conversion units, and a second signal based on a sum ofelectric charges accumulated in the plurality of photoelectricconversion units; a combining unit configured to generate a plurality offirst combining signals by combining mutually the first signals of theplurality of pixels, and a plurality of second combining signals bycombining mutually the second signals of the plurality of pixels; and anoutput unit configured to output only one or some of the plurality offirst combining signals generated by the combining unit.

According to an another aspect of the present invention, an imagingapparatus comprises: a plurality of pixels, arranged in a matrix, eachincluding a plurality of photoelectric conversion units generating anelectric charge based on an incident light and a pixel amplifying unitoutputting a signal based on the electric charge; a controlling unitconfigured to control the plurality of pixels to output a plurality offirst signals each based on a sum of the electric charge accumulated inones of the plurality of photoelectric conversion units in the pluralityof pixels, and to output a plurality of second signals each based on asum of the electric charge accumulated in the plurality of photoelectricconversion units in the plurality of pixels; a combining unit configuredto generate a plurality of first combining signals by combining mutuallythe first signals of the plurality of pixels, and a plurality of secondcombining signals by combining mutually the second signals of theplurality of pixels; and an output unit configured to output only one orsome of the plurality of first combining signals generated by thecombining unit.

According to a further aspect of the present invention, a driving methodof an imaging apparatus having a plurality of pixels, arranged in amatrix, each including a plurality of photoelectric conversion unitsgenerating an electric charge based on an incident light, comprises:outputting, by each of the plurality of pixels, a first signal based onan electric charge accumulated in one of the plurality of photoelectricconversion units, and a second signal based on a sum of electric chargesaccumulated in the plurality of photoelectric conversion units;generating a plurality of first combining signals by combining mutuallythe first signals of the plurality of pixels, and a plurality of secondcombining signals by combining mutually the second signals of theplurality of pixels; and outputting only one or some of the plurality offirst combining signals generated.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration example of animaging apparatus according to a first embodiment.

FIG. 2 is a conceptual view of the imaging apparatus according to thefirst embodiment.

FIG. 3 is a conceptual view of a read-out region.

FIG. 4 is a circuit diagram illustrating a configuration example of theimaging apparatus.

FIG. 5 is a timing chart of the imaging apparatus.

FIG. 6 is a timing chart illustrating horizontal read-out.

FIG. 7 is a conceptual view of an imaging apparatus according to asecond embodiment.

FIG. 8 is a conceptual view of a read-out region.

FIG. 9 is a circuit illustrating a configuration example of an imagingapparatus according to a third embodiment.

FIG. 10 is a timing chart of the imaging apparatus.

FIG. 11 is a circuit diagram illustrating a configuration example of animaging apparatus according to a fourth embodiment.

FIG. 12 is a view illustrating one example of an imaging system.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

First Embodiment

FIG. 1 is a block diagram illustrating a configuration example of animaging apparatus according to a first embodiment of the presentinvention; and FIG. 4 is a circuit diagram illustrating a configurationexample of the imaging apparatus. A pixel unit 100 is an imaging region,and has a plurality of pixels 10 which are arranged in a matrix form. Asis illustrated in FIG. 4, each of the plurality of pixels 10 hasphotoelectric conversion units 10-1 and 10-2, a floating diffusion 10-5,a pixel amplifier (pixel amplifying unit) 10-7, transfer switches 10-3and 10-4, a reset switch 10-6, and a selecting switch 10-8. Theplurality of photoelectric conversion units 10-1 and 10-2 are connectedto the same floating diffusion 10-5 through the plurality of transferswitches 10-3 and 10-4, respectively. The first photoelectric conversionunit 10-1 and the second photoelectric conversion unit 10-2 are, forinstance, photodiodes, each of which converts incident light into anelectric charge (electron) and accumulates the converted electric chargetherein. The first transfer switch 10-3 is turned on when a transfersignal PTX_A becomes a high level, and transfers the electric charge ofthe first photoelectric conversion unit 10-1 to the floating diffusion10-5. The second transfer switch 10-4 is turned on when a transfersignal PTX_B becomes a high level, and transfers the electric charge ofthe second photoelectric conversion unit 10-2 to the floating diffusion10-5. The pixel amplifier 10-7 amplifies the voltage of the floatingdiffusion 10-5, and outputs the amplified voltage from an outputterminal (source terminal). The selecting switch 10-8 is turned on whena selecting signal PSEL becomes a high level, and connects the outputterminal of the pixel amplifier 10-7 with a vertical output line VL_1.The pixel 100 in the first column is connected to a common verticaloutput line VL_1. The pixel 100 in the second column is connected to acommon vertical output line VL_2. The reset switch 10-6 is turned onwhen a reset signal PRES becomes a high level, and resets thephotoelectric conversion units 10-1 and 10-2 and the floating diffusion10-5 to a power source voltage. A vertical scanning circuit 11 suppliesthe reset signal PRES, the transfer signals PTX_A and PTX_B, and theselecting signal PSEL, to the pixels 100 in a matrix form one row by onerow. The pixel 10 outputs a signal according to the voltage of thefloating diffusion 10-5.

An adding circuit 12 has a capacitor 12-1 and a switch SW4; and addssignals of the vertical output lines VL_1 and VL_2 of two columns basedon a signal of a driving circuit 15 and outputs the added signal, ordoes not add the signals and outputs the intact signal. A first columnsignal processing circuit 13 has an amplifier 13-1, a feedback capacitor13-2, an input capacitor 13-3, a feedback switch SW2 and an input switchSW1. A second column signal processing circuit 13 has switches SW3 andSW2′ in place of the switches SW1 and SW2 in the column signalprocessing circuit 13 of the first column. The column signal processingcircuit 13 may be a circuit which simply amplifies a signal, or may alsobe a circuit which performs correlated double sampling (CDS) thatperforms differential processing between a pixel signal and a noisesignal. In the differential amplifier 13-1, a negative input terminal isconnected to the input capacitor 13-3, and a positive input terminal isconnected to a node of a reference voltage VREF. The differentialamplifier 13-1 outputs a signal obtained by inverting and amplifying asignal which is input into the negative input terminal.

An output signal amp_out of the column signal processing circuit 13 isinput into a column ADC circuit (column analog to digital conversionunit) 14. A column ADC circuit 14 converts an analog signal amp_outwhich is input from the column signal processing circuit 13 into adigital signal, based on a signal sent from a driving circuit 15. Thecolumn ADC circuit 14 has a comparator 14-1, a ramp source 14-2 which iscommon to each column, and a common counter 14-3 that is common to eachof the columns. The comparator 14-1 compares the signal amp_out with aramp signal (reference signal) RAMP of the ramp source 14-2, and outputsan inverted signal when the ramp signal RAMP becomes larger than thesignal amp_out. The counter 14-3 counts a count value “count” from thetime when the generation of the ramp signal RAMP has been started, untilthe output signal of the comparator 14-1 is inverted. The count value(digital value) “count” of the counter 14-3 is retained in an N-memory16-1 or an S-memory 16-2. In the N-memory 16-1, the noise signal isretained which is based on the noise level of the pixel 10. In theS-memory 16-2, the pixel signal is retained which is based on aphotoelectrically converted signal that has been generated by the pixel10. The N-memory 16-1 and the S-memory 16-2 each have a memory forwriting information sent from the comparator 14-1 therein, and memoriesfor read-out, which are connected to horizontal read-out lines S_out andN_out, respectively. The signal retained in the memory for writing istransferred to the memory for read-out, and then is horizontallytransferred and output to the horizontal read-out lines S_out and N_out,by the scan of a horizontal scanning circuit 17.

FIG. 2 is a conceptual view of the imaging apparatus. In FIG. 2, thepixel 10 has the two photoelectric conversion units 10-1 and 10-2 whichhave been divided into two in a horizontal direction under onemicrolens, and are described as photoelectric conversion units A and Brespectively. The photoelectric conversion unit A corresponds to thephotoelectric conversion unit 10-1, and the photoelectric conversionunit B corresponds to the photoelectric conversion unit 10-2. The pixelsignal of the photoelectric conversion unit A is referred to as an Asignal, and the pixel signal of the photoelectric conversion unit B isreferred to as a B signal. Furthermore, a signal based on an addedsignal of photoelectrically converted signals of the two photoelectricconversion units A and B is expressed as an A+B signal. In order todetect a focus, it is necessary to extract the A signal and the Bsignal, and to measure a phase difference between the signals. In thepresent embodiment, the A signal and the A+B signal are read out, andthe B signal is extracted from a difference between the A+B signal andthe A signal, by a not-shown processing circuit. Here, in order toincrease the speed at which the signal is read out, the proximate Asignals are and proximate A+B signals are added up by the adding circuit12. The sum of electric charges is obtained which are accumulated in onephotoelectric conversion unit in each of the pixels. Specifically, ahorizontal scanning period can be shortened, by reducing the number ofdata to be scanned by the horizontal scanning circuit 17. In FIG. 2, asolid line which connects the photoelectric conversion units A and B toeach other shows a combination of signals to be added. The specificmethod will be described later. In FIG. 2, two A signals are and two A+Bsignals are added to each other, but the number is not limited to two,but more than two signals may be added to each other. Furthermore, the Asignal is necessary for measuring the phase difference, and accordinglyis read out only from a region in which the phase difference isdetected. Specifically, the A signal is output from a part of columns.Thereby, the number of signals to be read out can be reduced, and thehorizontal scanning period of the horizontal scanning circuit 17 can beshortened. The A signal is a first signal which is output by the pixel10, and the A+B signal is a second signal which is output by the pixel10.

FIG. 3 is a view illustrating an example of a focus detection region 21in which a phase difference is measured and a focus is detected, in apixel unit 100. The pixel unit 100 has an OB region (optical blackregion) 22 in which the pixel 10 is light-shielded, and an apertureregion 20 that can receive incident light. The focus detection region 21is a region which is sandwiched between the dotted lines, and has pixelsin a part of the OB region 22 and pixels in a part of the apertureregion 20. An (A+A) signal is read out in the focus detection region 21.The (A+A) signal is a first combined signal obtained by combining the Asignals of the two pixels 10 with each other. The (A+A) signal is notread out from another region than the focus detection region 21. Theabove described imaging signal does not necessarily need to be read outfrom the whole region of the pixel unit 100 but may be read out from apart of a region containing the OB region 22 and the aperture region 20.In this case, in a region in a part of the pixel unit 100, a focusdetection region 21 is provided which is narrower than the region in thepart, and the (A+A) signal is read out therefrom. In the whole region ofthe pixel unit 100, the (A+B)+(A+B) signal is read out as the imagingsignal, which is a signal obtained by adding the A+B signals of the twoclose pixels 10. The (A+A) signal is a second combined signal obtainedby combining the A signals of the pixels 10 with each other.

FIG. 5 is a timing chart illustrating a method for driving the imagingapparatus. A timing example will be described below in the case wherethe two pixels 10 provided in the vicinity in the horizontal directionare added by the adding circuit 12. In the present embodiment, in orderto add the signals of the two pixels 10, the switch SW4 shall be turnedon, and the switch SW3 shall be turned off. When the signals of the twopixels 10 are not added and the signal of each of the pixels 10 is readout, the switch SW4 shall be turned off, and the switch SW3 shall beturned on.

Firstly, the selecting signal PSEL becomes a high level, the selectingswitch 10-8 is turned on, and the row of the pixel 10 to be output isselected. In addition, the reset signal PRES is set at a high level, andthereby the floating diffusion 10-5 is reset to a power sourcepotential. At this time, the switches SW2 and SW2′ shall be also turnedon, and the amplifier 13-1 shall be set at a reset state.

At the time t1, the reset signal PRES transitions to a low level, andthe reset switch 10-6 is turned off. Then, the noise signals of thepixels 10 in the reset state are output to the vertical output linesVL_1 and VL_2. At this time, both of the switch SW1 and switch SW4 areturned on, and accordingly two signals which are the signal of thevertical output line VL_1 and the signal of the vertical output lineVL_2 are added through the capacitors 13-3 and 12-1, respectively.

At the time t2, the switches SW2 and SW2′ are turned off, and therebythe column signal processing circuit 13 retains a signal obtained byadding the noise signals of the two pixels 10 in the reset state, andoutputs the signal amp_out to the column ADC circuit 14.

At the time t3, the ramp source 14-2 starts the generation of the rampsignal RAMP, and the counter 14-3 starts the count-up of the count value“count”. When the ramp signal RAMP becomes larger than the signalamp_out, the comparator 14-1 inverts the output signal. At the timing,the count value “count” of the counter 14-3 is written in the N-memory16-1. The digital signal based on the signal obtained by adding thesignals of the two pixels 10 in the reset state is retained in theN-memory 16-1. After that, the switches SW1 and SW4 are turned off. Thecounter 14-3 resets the ramp signal RAMP to an initial value, and resetsthe count value “count”.

Next, at the time t4, the transfer signal PTX_A is set at a high level,and the transfer switch 10-3 is turned on. The electric charge which hasbeen accumulated in the photoelectric conversion unit 10-1 istransferred to the floating diffusion 10-5. At the time t5, the PTX_A isset at a low level, and the transfer switch 10-3 is turned off. The Asignals based on the amounts of the electric charges which have beenaccumulated in the photoelectric conversion units 10-1 in the two pixels10 are output to the vertical output lines VL_1 and VL_2, respectively.

At the time t6, the switches SW1 and SW4 are turned on. The A signals ofthe vertical output lines VL_1 and VL_2 are added by the adding circuit12 and the column signal processing circuit 13, and the (A+A) signal isgenerated. The generated (A+A) signal is input into the column ADCcircuit 14.

At the time t7, the ramp source 14-2 starts the generation of the rampsignal RAMP, and the counter 14-3 starts the count-up of the count value“count”. When the ramp signal RAMP becomes larger than the signalamp_out, the comparator 14-1 inverts the output signal. At the timing,the count value “count” of the counter 14-3 is written in the S-memory16-2. The digital signal based on the (A+A) signal is retained in theS-memory 16-2. The digital signals in the S-memories 16-2 in each of thecolumns are sequentially horizontally transferred to the horizontalread-out line S_out, and the digital signals in the N-memories 16-1 ineach of the columns are sequentially horizontally transferred to thehorizontal read-out line N_out. After that, the switches SW1 and SW4 areturned off.

At the time t8, the transfer signals PTX_A and PTX_B are simultaneouslyset at a high level, and the transfer switches 10-3 and 10-4 are turnedon. At this time, an electric charge obtained by adding an electriccharge which has been accumulated in the photoelectric conversion unit10-1 to an electric charge which has been accumulated in thephotoelectric conversion unit 10-2 is retained in the floating diffusion10-5.

At the time t9, the transfer signals PTX_A and PTX_B are simultaneouslyset at a low level, and the transfer switches 10-3 and 10-4 are turnedoff. Signals based on the A+B signals obtained by adding thephotoelectrically converted signals of the two photoelectric conversionunits 10-1 and 10-2 on the floating diffusions 10-5 are output to thevertical output lines VL_1 and VL_2, respectively.

At the time t10, the switches SW1 and SW4 are turned on. The two A+Bsignals of the vertical output lines VL_1 and VL_2 are added by theadding circuit 12 and the column signal processing circuit 13, and the(A+B)+(A+B) signal is generated. The generated (A+B)+(A+B) signal isinput into the column ADC circuit 14.

At the time t11, the ramp source 14-2 starts the generation of the rampsignal RAMP, and the counter 14-3 starts the count-up of the count value“count”. When the ramp signal RAMP becomes larger than the signalamp_out, the comparator 14-1 inverts the output signal. At the timing,the count value “count” of the counter 14-3 is written in the S-memory16-2. The digital signal based on the (A+B)+(A+B) signal is retained inthe S-memory 16-1. The digital signals in the S-memories 16-2 in each ofthe columns are sequentially horizontally transferred to the horizontalread-out line S_out, and the digital signals in the N-memories 16-1 ineach of the columns are sequentially horizontally transferred to thehorizontal read-out line N_out.

The operations in between the times t4 and t8, which have been describedabove, are operations of a first mode. In between the times t4 and t5,the vertical scanning circuit (controlling unit) 11 makes the pluralityof pixels 10 output the A signal, in the state in which onephotoelectric conversion unit 10-1 out of the plurality of photoelectricconversion units 10-1 and 10-2 is connected to the floating diffusion10-5. In between the times t6 and t8, the adding circuit (combiningunit) 12 adds (combines) the output signals in every pixel 10 in aplurality of columns in the same row, and outputs the (A+A) signal.Specifically, the adding circuit 12 connects the output lines VL_1 andVL_2 of the pixels 10 in the plurality of columns to the same nodethrough the capacitors 13-3 and 12-1 respectively, and thereby adds(combines) the signals. After that, in a period p1 in FIG. 6, thehorizontal scanning circuit (output unit) 17 selects and outputs a part(signal based on focus detection region 21) of the (A+A) signals whichhave been added by the adding circuit 12.

Operations after the time t8 are operations of a second mode. In betweenthe times t8 and t9, the vertical scanning circuit (controlling unit) 11makes the plurality of pixels 10 output the A+B signal, in the state inwhich the plurality of photoelectric conversion units 10-1 and 10-2 areconnected to the floating diffusion 10-5. After the time t10, the addingcircuit (combining unit) 12 adds (combines) the output signals in everypixel 10 in a plurality of columns in the same row, and outputs the(A+B)+(A+B) signal. After that, in a period p2 in FIG. 6, the horizontalscanning circuit (output unit) 17 outputs the (A+B)+(A+B) signals(signals of whole region in pixel unit 100) which have been added by theadding circuit 12.

The feature of the present embodiment exists in a point that the (A+A)signal is generated by adding the A signals which have been read outfrom the pixels 10 in the plurality of columns to each other, and thatthe (A+B)+(A+B) signal is generated by adding the A+B signals which havebeen read out from the pixels 10 in the plurality of columns to eachother. In addition, the feature of the present embodiment exists in apoint that added signals of the A signals in the whole region of thepixel unit 100 are not output but added signals of the A signals only inthe focus detection region 21 are output.

In the present embodiment, a procedure for obtaining the A+B signal isnot limited to the adding operation to be carried out on the floatingdiffusion 10-5. For information, the S-memory 16-2 may have individualmemories for the A signal and the A+B signal, or may use a common memoryin a time-division fashion.

FIG. 6 is a timing chart of the horizontal transfer read-out of thehorizontal scanning circuit 17. The horizontal read-out lines N_out andS_out show each 1 bit of the digital data. The transfer pulses pt1 topt26 are pulses which are input to the N-memory 16-1 and the S-memory16-2 in each of the columns from the horizontal scanning circuit 17. Thesubscript of a pulse name pt designates the number of the column. Thetransfer pulses pt7 to pt19 show a horizontal zone of the focusdetection region 21 which is sandwiched between the dotted lines in FIG.3.

In the period p1, the digital value of the A+A signal is retained in theS-memory 16-2. In the period p2, the digital value of the (A+B)+(A+B)signal is retained in the S-memory 16-2. The period p1 is a period inwhich the A+A signal is output. In the period p1, the horizontalscanning circuit 17 scans only the columns corresponding to the focusdetection region 21, and accordingly sequentially scans the transferpulses pt7 to pt19 of the corresponding columns. Thereby, the digitalvalues of the A+A signals only in the focus detection region 21 aresequentially output, and accordingly the read-out speed becomes fast.

The period p2 is a period in which the digital value of the (A+B)+(A+B)signal is output. In the period p2, in order to scan all the columns inthe pixel unit 100, the horizontal scanning circuit 12 sequentiallyscans the transfer pulses pt1 to pt26 of the corresponding columns.Thereby, the digital values of the (A+B)+(A+B) signals in the wholeregion in the pixel unit 100 are sequentially output.

The digital values of the (A+A) signals and the digital values of the(A+B)+(A+B) signals can be retained in the common S-memory 16-2 in atime-division fashion. In the present embodiment, the A signals in theplurality of columns are added thereby to generate the (A+A) signals,and the (A+B) signals in the plurality of columns are added thereby togenerate the (A+B)+(A+B) signals. When the (A+A) signal is generated,the A signal only in the pixel 10 in the focus detection region 21 isread out, thereby the number of the data to be read out is reduced, andthe read-out speed can be increased. In the present embodiment, such amethod has been described above that an analog signal in every column isconverted into a digital signal and the digital signal is read out, butthe method may be a form of outputting the analog signal withoutconverting the analog signal to the digital signal.

The imaging apparatus according to the present embodiment shows aneffect capable of reading out a signal having a high S/N in a shortperiod of time, by combining the following operations (1) to (3).

(1) The imaging apparatus reads out a signal for detecting a focus(detecting phase difference) from the pixel 10 as the A signal, andreads out the imaging signal as the A+B signal.

(2) The imaging apparatus reads out the A signal in addition to the A+Bsignal in the pixel in the focus detection region 21 in which the focusis detected, and does not read out the A signal in the pixel in a region(region other than focus detection region 21) in which the focus is notdetected.

(3) The imaging apparatus adds the A signals of the pixels 10 in theplurality of columns to each other, and adds the A+B signals of thepixels 10 in the plurality of columns to each other.

By the operation (2), the imaging apparatus can reduce the amount of thedata, and can increase the read-out speed. A signal of the A signal issmall compared to that of the A+B signal, and the B signal which isobtained by subtracting the A signal from the A+B signal has a furtherdegraded S/N. Accordingly, those signals become the factor of degradinga focus detection accuracy, when the illuminance is low. The imagingapparatus according to the present embodiment enhances the S/N of the Asignal by adding the A signals in the plurality of columns, and canenhance the focus detection accuracy when the illuminance is low. Inaddition, the imaging apparatus can obtain an imaging signal having ahigh S/N ratio by adding the A+B signals in the plurality of columns.

For information, the position of the focus detection region 21 may bedifferentiated according to each frame.

Second Embodiment

FIG. 7 is a conceptual view of an imaging apparatus according to asecond embodiment of the present invention, which corresponds to FIG. 2.FIG. 8 is a view illustrating an example of a focus detection region 21in a pixel unit 100, similarly to FIG. 3. An imaging apparatus accordingto the present embodiment has the same configuration and driving timingas those in that of the first embodiment, and has a different focusdetection region from that in the first embodiment. In the presentembodiment, a focus detection region in which the focus is detected isthe aperture region 20, and a region in which the focus is not detectedis the OB region 22. The (A+B)+(A+B) signals are generated based on thepixels in the whole region of the pixel unit 100. The A+A signal isgenerated only based on the pixels in the aperture region 20, and is notgenerated in the OB region 22. In the OB region 22, the (A+B)+(A+B)signal is generated which is obtained by adding the A+B signals in theplurality of columns. In the aperture region 20, the (A+B)+(A+B) signalwhich is obtained by adding the A+B signals in the plurality of columns,and the (A+A) signal that is obtained by adding the A signals in theplurality of columns, are generated. The A+A signal is not read out inthe OB region in which the focus is not detected, accordingly the amountof the data is reduced and the data can be read out at high speed.

In addition, the imaging apparatuses according to the first and secondembodiments combine the signals which have been output from therespective pixel amplifiers 10-7 in the pixels 10 to each other andgenerate the (A+A) signal and the (A+B)+(A+B) signal. As anotherexample, the pixel amplifier 10-7 may combine the electric charges ofthe floating diffusions 10-5 in the plurality of pixels 10 with eachother, and output each of the (A+A) signal and the (A+B)+(A+B) signal.

Third Embodiment

FIG. 9 is a view illustrating a configuration example of a part of animaging apparatus according to a third embodiment of the presentinvention, similarly to FIG. 4. The present embodiment is different fromthe first embodiment in a method for combined signals of the pixels inthe plurality of columns. The imaging apparatus according to the presentembodiment averages the signals in a capacitor, as a method forcombining the signals of the pixels in the plurality of columns. Thepoint will be described below in which the present embodiment isdifferent from the first embodiment. A first signal holding circuit 18is connected to the vertical output line VL_1, and has capacitors 18-1and 18-2, and switches SW6 to SW9. A second signal holding circuit 18 isconnected to the vertical output line VL_2, and has capacitors 18-1 and18-2, and switches SW10 to SW13. The adding circuit 12 has a switch SW5.When the switch SW5 is turned on, the signal of the vertical output lineVL1 and the signal of the vertical output line VL2 are averaged(combined). The output terminals of the signal holding circuits 18 areconnected to the column signal processing circuit 13 in FIG. 4. Forinformation, the switches SW8 and SW12 may be each connected to thecomparator 14-1 or to the N-memory 16-1 in FIG. 4. Similarly, theswitches SW9 and SW13 may be each connected to the comparator 14-1 or tothe S-memory 16-2 in FIG. 4.

FIG. 10 is a timing chart illustrating a method for driving an imagingapparatus of FIG. 9. An example will be described below in which signalsof two pixels 10 are averaged (combined). In order to average (combine)the signals of the two pixels 10, the switch SW5 is turned on, and theswitches SW10 and SW11 are turned off. A signal out_n corresponds to anoutput signal amp_out of the column signal processing circuit 13 whichis connected to the switch SW8. A signal out_s corresponds to the outputsignal amp_out of the column signal processing circuit 13 which isconnected to the switch SW9.

Firstly, the selecting signal PSEL becomes a high level, then theselecting switch 10-8 is turned on, and the row of a pixel 10 isselected. In addition, when the reset signal PRES is set at a highlevel, the reset switch 10-6 is turned on, and the floating diffusion10-5 is reset to a power source voltage.

At the time t12, the reset signal PRES is transited to a low level, thenthe reset switch 10-6 is turned off, and signals of the pixels 10 basedon the reset state are output to the vertical output lines VL_1 andVL_2. At this time, the switches SW6 and SW5 are turned on, andaccordingly the vertical output lines VL_1 and VL_2 are connected toeach other. At this time, the approximately average value of thevoltages of the vertical output lines VL_1 and VL_2 based on theeffective resistance value of the transistors 10-7 and 10-8 isaccumulated in a capacitor 18-1. When the voltage values of the verticaloutput lines VL_1 and VL_2 are close to each other, this average valuewhich is extremely close to a true average value is accumulated in thecapacitor 18-1. When the voltage values of the vertical output linesVL_1 and VL_2 are distant from each other, a value obtained by weightingthe voltages of the vertical output lines VL_1 and VL_2 with the highvoltage is accumulated in the capacitor 18-1. When the pixels 10 are inthe reset state, the voltages of the vertical output lines VL_1 and VL_2are generally close values to each other.

At the time t13, the switch SW6 is turned off, and the electric chargeis retained in the capacitor 18-1. At the time t14 immediately after thetime t13, the switch SW8 is turned on, and the signal retained in thecapacitor 18-1 is output. After that, the switch SW8 is turned off.

At the time t15, the transfer signal PTX_A is set at a high level, andthe transfer switch 10-3 is turned on. The electric charge which hasbeen accumulated in the photoelectric conversion unit 10-1 istransferred to the floating diffusion 10-5. At the time t16, thetransfer signal PTX_A is set at a low level, then the transfer switch10-3 is turned off, and the above described transfer is ended. Inaddition, a switch SW7 is turned on, and thereby an (A+A)/2 signal whichis an approximately average value of the voltages of the vertical outputlines VL_1 and VL_2 is retained in a capacitor 18-2. At the time t18,the switch SW9 is turned on, and the signal retained in the capacitor18-2 is output.

At the time t19, the transfer signals PTX_A and PTX_B are simultaneouslyset at a high level, and the transfer switches 10-3 and 10-4 are turnedon. At this time, an electric charge obtained by adding the electriccharge which has been accumulated in the photoelectric conversion unit10-1 and the electric charge which has been accumulated in thephotoelectric conversion unit 10-2 results in being retained in thefloating diffusion 10-5. To the vertical output lines VL_1 and VL_2,each of the A+B signals is output which has been obtained by adding thephotoelectrically converted signals of the two photoelectric conversionunits 10-1 and 10-2 on the floating diffusion 10-5. In addition, whenthe switch SW7 is turned on, a signal obtained by averaging the voltagesof the vertical output lines VL_1 and VL_2, specifically, an[(A+B)+(A+B)]/2 signal is written in the capacitor 18-2.

At the time t20, the transfer signals PTX_A and PTX_B are set at a lowlevel, then the transfer switches 10-3 and 10-4 are turned off, and theabove described transfer is ended. At the time t21, the switch SW7 isturned off, and the capacitor 18-2 retains the signal [(A+B)+(A+B)]/2.At the time t22, the switch SW9 is turned on, and the signal retained inthe capacitor 18-2 is output.

The operations in between the times t15 and t19, which have beendescribed above, are operations of the first mode. In between the timest15 and t16, the vertical scanning circuit (controlling unit) 11 makesthe plurality of pixels 10 output the A signal in the state in which onephotoelectric conversion unit 10-1 out of the plurality of photoelectricconversion units 10-1 and 10-2 is connected to the floating diffusion10-5. The adding circuit (combining unit) 12 averages (combines) theoutput signals in every pixel 10 in the plurality of columns in the samerow, and outputs an (A+A)/2 signal. Specifically, the adding circuit 12connects the output lines VL_1 and VL_2 of the pixels in the pluralityof columns to each other, and thereby averages (combines) the signals.After that, in the period p1 in FIG. 6, the horizontal scanning circuit(output unit) 17 selects a part of the (A+A)/2 signals (signals based onfocus detection region 21) which have been averaged by the addingcircuit 12, and outputs the signal.

Operations after the time t19 are the operations of the second mode. Inbetween the times between t19 and t20, the vertical scanning circuit(controlling unit) 11 makes the plurality of pixels 10 output the A+Bsignal in the state in which the plurality of photoelectric conversionunits 10-1 and 10-2 are connected to the floating diffusion 10-5. Afterthe time t20, the adding circuit (combining unit) 12 averages (combines)the output signals in every pixel 10 in the plurality of columns in thesame row, and outputs the [(A+B)+(A+B)]/2 signal. After that, in aperiod p2 in FIG. 6, the horizontal scanning circuit (output unit) 17outputs the [(A+B)+(A+B)]/2 signals (signals of whole region in pixelunit 100) which have been averaged by the adding circuit 12.

Thereby, an averaging process of the A signals in the plurality ofcolumns and the averaging process of the A+B signals in the plurality ofcolumns are performed. The imaging apparatus according to the presentembodiment generates the average value of the A signals only in thefocus detection region 21, similarly to the first embodiment, therebyreduces the number of the data to be read out, and can read out the dataat high speed. In addition, the imaging apparatus according to thepresent embodiment can obtain an effect of reducing the number of data,by the averaging process. In addition, the imaging apparatus accordingto the present embodiment can carry out the adding or averaging processwithout arranging an active circuit for the adding or averaging process.The averaging process in the present embodiment has been performed byconnecting the vertical output lines VL_1 and VL_2, but may also beperformed by reading out the signals to the capacitors for the verticaloutput line VL_1 and the capacitors for the vertical output line VL_2respectively, and short-circuiting each pair of capacitors. The addingcircuit 12 in FIG. 9 has an effect of reducing a time period in whicheach pair of capacitors are short-circuited, reducing the number of thecapacitors necessary for the averaging process, and assigning thereduced capacitors to another process, compared to the above describedcase where each pair of capacitors are short-circuited.

In addition, in the first to third embodiments, the A signals of thepixels 10 in the same row have been combined with each other and the A+Bsignals similarly have been combined with each other. As anotherexample, it is also acceptable to combine the A signals of the pixels 10in a plurality of rows with each other and the A+B signals similarlywith each other. When the above described A signals and A+B signals ofthe pixels 10 in the plurality of rows are combined with each other, itis acceptable that the vertical scanning circuit 11 simultaneouslyselects the pixels 10 in the plurality of rows, and the pixels 10 in theplurality of rows are simultaneously output to the vertical output lineVL_1.

Fourth Embodiment

FIG. 11 is a view illustrating a configuration example of an imagingapparatus according to a fourth embodiment of the present invention. Inthe present embodiment, digital data in the plurality of columns isadded. The point will be described below in which the present embodimentis different from the first embodiment. The present embodiment isdifferent from the first embodiment in the point that digital data afteran analog signal has been converted to a digital signal is added to eachother. FIG. 11 is a view of an imaging apparatus in which the capacitor12-1 and the switch SW4 are deleted from, and an adding circuit 19 isadded to the imaging apparatus in FIG. 4. A memory 16-1 a for writingand a memory 16-1 b for read-out correspond to an N-memory 16-1 in FIG.4. A memory 16-2 a for writing and a memory 16-2 b for read-outcorrespond to an S-memory 16-2 in FIG. 4. The adding circuit (combiningunit) 19 adds (combines) digital data of the memories 16-1 a for writingin the plurality of columns, and writes the added digital data in thememory 16-1 b for read-out. In addition, the adding circuit (combiningunit) 19 adds (combines) digital data of the memories 16-2 a for writingin the plurality of columns, and writes the added digital data in thememory 16-2 b for read-out. When the A signals have been read out fromthe pixels 10, the A+A signal obtained by adding the A signals in theplurality of columns is retained in the memory 16-2 b for read-out. Inaddition, when the A+B signals have been read out from the pixels 10,the (A+B)+(A+B) signal obtained by adding the A+B signals in theplurality of columns is retained in the memory 16-2 b for read-out. Theimaging apparatus according to the present embodiment generates the A+Asignal only in the focus detection region 21, similarly to that in thefirst embodiment, thereby reduces the number of the data to be read out,and can read out the data at high speed.

In addition, in the present embodiment, the A signals of the pixels 10in the same row have been combined with each other and the A+B signalshave been similarly combined with each other. As another example, it isalso acceptable to combine the A signals of the pixels 10 in a pluralityof rows with each other and combine the A+B signals similarly with eachother. For instance, the adding circuit 19 may combine the A signals ofdigital data of the pixels 10 in the plurality of rows with each other,and similarly combine the A+B signals to each other. Incidentally, inthe present exemplary embodiment, an example has been described in whichthe digital signals are added to each other, as one example ofcombination of the digital signals. As another example, the combinationof the digital signals may be the averaging of the digital signals.

Fifth Embodiment

FIG. 12 is a view illustrating a configuration example of an imagingsystem according to a fifth embodiment of the present invention. Theimaging system has the imaging apparatus 154 according to the first tofourth embodiments. Examples of the imaging system include a digitalcamera, a digital camcorder and a monitoring camera. FIG. 12 illustratesthe case where the imaging apparatus 154 is applied to the digitalcamera, as an example of the imaging system.

The imaging system has a lens 152 for making the imaging apparatus 154form an optical image of an object thereon, a barrier 151 for protectingthe lens 152, and a diaphragm 153 for varying the quantity of lightwhich has passed through the lens 152. The lens 152 and the diaphragm153 form an optical system which guides the light to the imagingapparatus 154. The imaging system also has an output signal processingunit 155 which performs the process of the output signal which theimaging apparatus 154 outputs. The output signal processing unit 155 hasa digital signal processing unit, and performs an operation of variouslycorrecting the signals which the imaging apparatus 154 outputs,compressing the signals, as needed, and outputting the compressedsignals.

The imaging system also has a buffer memory unit 156 for temporarilymemorizing image data, and a recording medium controlling interface unit158 for recording signals in or reading signals from a recording medium.The imaging system further has a releasable recording medium 159 such asa semiconductor memory, for recording the image data therein or readingthe image data therefrom. The imaging system further has an externalinterface unit 157 for communicating with an external computer or thelike, an overall control/calculation unit 1510 which performs variouscalculations and controls the whole digital camera, and the imagingapparatus 154. The imaging system further has a timing generator 1511which outputs various timing signals to the imaging apparatus 154 andthe output signal processing unit 155. Here, the timing signal and thelike may be input from the outside. The imaging system may have at leastthe imaging apparatus 154 and the output signal processing unit 155which processes an output signal that has been output from the imagingapparatus 154. In addition, the output signal processing unit 155 candetect a focus of the optical system by using the (A+A) signal or the(A+A)/2 signal for phase difference detection, which the imagingapparatus 154 outputs. Furthermore, the output signal processing unit155 can generate an image by using the (A+B)+(A+B) signal or the[(A+B)+(A+B)]/2 signal which the imaging apparatus 154 outputs. As hasbeen described above, the imaging system of the present embodiment hasthe imaging apparatus 154 applied thereto, and can detect the focus ofthe optical system and generate the image.

For information, in the first to fifth embodiments, a checkered filterof RGBG can be used as a color filter for the pixels 10. When the colorfilter is provided on each of the pixels 10 of the imaging apparatus,the photoelectrically converted signals sent from the pixels of the samecolor can be added to each other.

Note that the above embodiments are merely examples how the presentinvention can be practiced, and the technical scope of the presentinvention should not be restrictedly interpreted by the embodiments. Inother words, the present invention can be practiced in various wayswithout departing from the technical concept and main features of theinvention.

The present invention can provide an imaging apparatus which has anincreased speed of an operation.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2013-176799, filed Aug. 28, 2013, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An imaging apparatus comprising: a plurality of pixels, arranged in rows and columns, each including one microlens and a plurality of photoelectric conversion units generating an electric charge based on an incident light from the one microlens; a controlling unit configured to control each of the plurality of pixels to output a first signal based on an electric charge accumulated in one of the plurality of photoelectric conversion units, and a second signal based on a sum of electric charges accumulated in the plurality of photoelectric conversion units; a combining unit configured to generate a plurality of first combining signals by combining mutually the first signals of the plurality of pixels, and a plurality of second combining signals by combining mutually the second signals of the plurality of pixels; and an output unit configured to output the plurality of second combining signals which corresponds to the columns of the plurality of pixels, and a part of the plurality of first combining signals which correspond to a part of the columns of the plurality of pixels, without outputting the other part of the plurality of first combining signals.
 2. The imaging apparatus according to claim 1, wherein the combining unit adds mutually the first signals of the pixels between different columns, and adds mutually the second signals of the pixels between different columns.
 3. The imaging apparatus according to claim 1, wherein the combining unit averages mutually the first signals of the pixels between different columns, and averages mutually the second signals of the pixels between different columns.
 4. The imaging apparatus according to claim 1, further comprising a plurality of column output lines, to each of which the first and second signals are output respectively from the pixel, and the plurality of column output lines are arranged each corresponding to one of columns, wherein the combining unit generates the first and second combining signals by connecting the plurality of column output lines through a capacitor to a same node mutually.
 5. The imaging apparatus according to claim 2, further comprising a plurality of column output lines, to each of which the first and second signals are outputted respectively from the pixel, and the plurality of column output lines are arranged each corresponding to one of column, wherein the combining unit generates the first and second combining signals by connecting the plurality of column output lines through a capacitor to a same node mutually.
 6. The imaging apparatus according to claim 1, further comprising an analog to digital conversion unit configured to convert the first and second signals respectively to digital signals, wherein the combining unit generates the first and second combining signals by combining the digital signals generated by the analog to digital conversion unit.
 7. The imaging apparatus according to claim 2, further comprising an analog to digital conversion unit configured to convert the first and second signals respectively to digital signals, wherein the combining unit generates the first and second combining signals by combining the digital signals generated by the analog to digital conversion unit.
 8. The imaging apparatus according to claim 3, further comprising an analog to digital conversion unit configured to convert the first and second signals respectively to digital signals, wherein the combining unit generates the first and second combining signals by combining the digital signals generated by the analog to digital conversion unit.
 9. The imaging apparatus according to claim 1, further comprising a plurality of column output lines, to each of which the first and second signals are output respectively from the pixel, wherein the plurality of column output lines are arranged each corresponding to one of columns, and the combining unit performs the combining by connecting the plurality of column output lines.
 10. The imaging apparatus according to claim 3, further comprising a plurality of column output to each of which the first and second signals are output respectively from the pixel, wherein the plurality of column output lines are arranged each corresponding to one of columns, and the combining unit performs the combining by connecting the plurality of column output lines.
 11. An imaging apparatus comprising: a plurality of pixels, arranged in rows and columns, each including one microlens, a plurality of photoelectric conversion units generating an electric charge based on an incident light from the one microlens and a pixel amplifying unit outputting a signal based on the electric charge; a controlling unit configured to control the plurality of pixels so that a plurality of the pixel amplifying units output a plurality of first signals each based on a sum of the electric charge accumulated in ones of the plurality of photoelectric conversion units in the plurality of pixels, and output a plurality of second signals each based on a sum of the electric charge accumulated in the plurality of photoelectric conversion units in the plurality of pixels; a combining unit configured to generate a plurality of first combining signals by combining mutually the first signals of the plurality of pixels, and a plurality of second combining signals by combining mutually the second signals of the plurality of pixels; and an output unit configured to output the plurality of second combining signals which correspond to the columns of the plurality of pixels, and a part of the plurality of first combining signals which correspond to a part of the columns of the plurality of pixels, without outputting the other part of the plurality of first combining signals.
 12. An imaging system comprising: an imaging apparatus; an optical system configured to focus an optical image onto the imaging apparatus; and an output signal processing unit, wherein the imaging apparatus comprises: a plurality of pixels, arranged in rows and columns, each including one microlens and a plurality of photoelectric conversion units generating an electric charge based on an incident light from the one microlens; a controlling unit configured to control each of the plurality of pixels to output a first signal based on an electric charge accumulated in one of the plurality of photoelectric conversion units, and a second signal based on a sum of electric charges accumulated in the plurality of photoelectric conversion units; a combining unit configured to generate a plurality of first combining signals by combining mutually the first signals of the plurality of pixels, and a plurality of second combining signals by combining mutually the second signals of the plurality of pixels; and an output unit configured to output the plurality of second combining signals which correspond to the columns of the plurality of pixels, and a part of the plurality of first combining signals which correspond to a part of the columns of the plurality of pixels, without outputting the other part of the plurality of first combining signals, and wherein the output signal processing unit detects a focus based on the plurality of first combining signals, and on a difference signal based on a difference between the plurality of first combining signals and the plurality of second combining signals, and generates an image based on the plurality of second combining signals.
 13. An imaging system comprising: an imaging apparatus; an optical system configured to focus an optical image onto the imaging apparatus; and an output signal processing unit, wherein the imaging apparatus comprises: a plurality of pixels, arranged in rows and columns, each including one microlens, a plurality of photoelectric conversion units generating an electric charge based on an incident light from the one microlens, and a pixel amplifying unit outputting a signal based on the electric charge; a controlling unit configured to control the plurality of pixels so that a plurality of the pixel amplifying units output a plurality of first signals each based on a sum of the electric charge accumulated in ones of the plurality of photoelectric conversion units in the plurality of pixels, and output a plurality of second signals each based on a sum of the electric charge accumulated in the plurality of photoelectric conversion units in the plurality of pixels; a combining unit configured to generate a plurality of first combining signals by combining mutually the first signals of the plurality of pixels, and a plurality of second combining signals by combining mutually the second signals of the plurality of pixels; and an output unit configured to output the plurality of second combining signals which correspond to the columns of the plurality of pixels, and a part of the plurality of first combining signals which correspond to a part of the columns of the plurality of pixels, without outputting the other part of the plurality of first combining signals, wherein the output signal processing unit detects a focus based on the plurality of first combining signals and on a difference signal based on a difference between the plurality of first combining signals and the plurality of second combining signals, and generates an image based on the plurality of second combining signals.
 14. A driving method of an imaging apparatus having a plurality of pixels, arranged in rows and columns, each including one microlens and a plurality of photoelectric conversion units generating an electric charge based on an incident light from the one microlens, comprising: outputting, by each of the plurality of pixels, a first signal based on an electric charge accumulated in one of the plurality of photoelectric conversion units, and a second signal based on a sum of electric charges accumulated in the plurality of photoelectric conversion units; generating a plurality of first combining signals by combining mutually the first signals of the plurality of pixels, and a plurality of second combining signals by combining mutually the second signals of the plurality of pixels; and outputting the plurality of second combining signals which correspond to the columns of the plurality of pixels, and a part of the plurality of first combining signals which correspond to a part of the columns of the plurality of pixels, without outputting the other part of the plurality of first combining signal.
 15. The driving method according to claim 14, wherein the generating a plurality of first combining signals is performed by adding mutually the first signals of the pixels between different columns, and the generating a plurality of second combining signals is performed by adding mutually the second signals of the pixels between different columns.
 16. The driving method according to claim 14, wherein the generating a plurality of first combining signals is performed by averaging mutually the first signals of the pixels between different columns, and the generating a plurality of second combining signals is performed by averaging mutually the second signals of the pixels between different columns.
 17. The driving method according to claim 14, wherein a plurality of column output lines are provided, to each of which the first and second signals are output respectively from the pixel, the plurality of column output lines being arranged each corresponding to one of columns, and the first and second combining signals are generated by connecting the plurality of column output lines through a capacitor to a same node mutually.
 18. The driving method according to claim 14, further comprising converting the first and second signals respectively to digital signals, wherein the first combining signal is generated by combining the digital signals based on the first signal, and the second combining signal is generated by combining the digital signals based on the second signal.
 19. The imaging apparatus according to claim 1, wherein the output unit further outputs the plurality of the second combining signals.
 20. The imaging apparatus according to claim 11, wherein the output unit further outputs the plurality of the second combining signals.
 21. The imaging apparatus according to claim 1, further comprising an analog to digital conversion unit, wherein the combining unit generates the first and second combining signals as analog signals, and outputs the first and second combining signals to the analog to digital conversion unit, the analog to digital conversion unit converts the first and second combining signals respectively to digital signals, and the plurality of second combining signals and the part of the plurality of first combining signals output from the output unit are digital signals.
 22. The imaging apparatus according to claim 11, further comprising an analog to digital conversion unit, wherein the combining unit generates the first and second combining signals as analog signals, and outputs the first and second combining signals to the analog to digital conversion unit, the analog to digital conversion unit converts the first and second combining signals respectively to digital signals, and the plurality of second combining signals and the part of the plurality of first combining signals output from the output unit are digital signals.
 23. A driving method of an imaging apparatus having a plurality of pixels, arranged in rows and columns, each including one microlens and a plurality of photoelectric conversion units generating an electric charge based on an incident light from the one microlens, and the imaging apparatus further having memory units arranged corresponding to the columns and a horizontal scanning circuit, the driving method comprising: outputting, by each of the plurality of pixels, a first signal based on an electric charge accumulated in one of the plurality of photoelectric conversion units, and a second signal based on a sum of electric charges accumulated in the plurality of photoelectric conversion units; generating a plurality of first combining signals by combining mutually the first signals of the plurality of pixels, and a plurality of second combining signals by combining mutually the second signals of the plurality of pixels; holding, by the memory units, the plurality of second combining signals; holding, by at least a part of the memory units configured to hold the plurality of second combining signals, the plurality of first combining signals; scanning, by the horizontal scanning circuit, the part of the memory units holding the plurality of first combining signals without scanning the other part of the memory units; and scanning, by the horizontal scanning circuit, the memory units holding the plurality of second combining signals. 